The present invention relates to a circuit breaker having a base constituting a molded case employed to protect the electric cables and lines and a crossbar supported onto this base to hold a movable contact and, more particularly, a circuit breaker, for example, a molded case circuit breaker stipulated in IEC60947-2, that has a function of executing quick-make and quick-break of the movable contact by swinging the crossbar by virtue of an accumulated force of a toggle link mechanism regardless of an ON/OFF operation speed of a handle, and is excellent in the prevention of contact point deposition in the open/close operation and the concurrent closing of respective contacts.
As set forth in Patent Application Publication (KOKAI) Hei 09-161641, for example, the circuit breaker in the prior art comprises a molded case consisting of a base and a cover, a movable contact provided to the inside of the molded case to have a movable contact point, a fixed contact having a fixed contact point that is connected/disconnected to/from the movable contact point, a crossbar that is molded out of the insulating material and supported onto the base in the closed state of the circuit breaker to hold the movable contact swingably, a switching mechanism portion for opening/closing the movable contact via this crossbar, a spring for pushing the movable contact point against the fixed contact point in the closed state of the circuit breaker, etc.
The contact points are worn away and eroded away by the arc that is generated by the repetition of the opening/closing operations and the opening/closing in the current supply in the actual use due to the electrical and mechanical or both factors. In order to maintain the stability of contact between the contact points even when the contact points are worn away and eroded away in this manner, a predetermined overtravel is provided. Where the xe2x80x9covertravelxe2x80x9d is an amount of movement of the movable contact point before and after the removal, i.e., an amount that indicates the contacting margin of the contact point when the fixed contact and the fixed contact point are removed in the closed state of the circuit breaker, and is about one to two times a thickness of the contact point.
The crossbar and the base as constituent parts of the circuit breaker, that are formed of thermosetting resin as a principal component, were employed since the mechanical strength, the thermal resistance, the insulating property, etc. are required of them. For example, as the 30 ampere-frame circuit breaker, the crossbar was molded out of the material containing phenol 52 wt %, glass fiber 15 wt %, inorganic filler 10 wt %, wood flour 15 wt %, and pigment and others 8 wt %, and the base was molded out of the material containing phenol 50 wt %, wood flour 30 wt %, inorganic filler 15 wt %, and pigment and others 5 wt %.
In the circuit breaker in the prior art, since the base that occupies most of the volume of the plastic parts is constructed by the thermosetting resin such as phenol resin, unsaturated polyester resin, etc. as a principal component, the reduction in thickness of the parts is difficult to disturb the reduction in size and the reduction in weight.
In particular, in the base constructed by the thermosetting resin as a principal component, portions constituting the base interior need a predetermined thickness or more because of the molding restriction irrespective of the size of the base. Thus, such portions constituting the base interior are formed excessively thick and thus the reduction in size of the base becomes difficult. For example, in the small circuit breaker having 225 ampere-frame or less in which the interpole pitch is less than 35 mm, the pressure of the spring between the contact points is less than 20 N, etc., the rib having a height of more than 2 mm needs the thickness of more than about 2 mm because of the molding restriction and thus the portions constituting the base interior are formed excessively thick. Here the rib thickness of 2 mm is such a value that is decided with a minute margin to satisfy the minimum thickness standard of more than 1 mm to 3 mm of the thermosetting resin, that is normally well known.
Also, since the base of the circuit breaker in the prior art contains the thermosetting resin as a principal component, the flash generated in the molding, the sprue and the runner generated in the injection molding, etc. must be destroyed by fire or buried under the ground.
Then, for the reasons that the molding precision of details can be increased, etc., it is examined to employ the moldings that contain the thermoplastic resin as a principal component. However, if the thermoplastic resin is applied particularly to the base, such resin did not sufficiently satisfy the characteristics that are required for the base. For example, the moldings containing the thermoplastic resin set forth in Patent Application Publication (KOKAI) Hei 08-171847, the inorganic compound that has the dehydration reaction at 200xc2x0 C. or more, and the reinforcement is excellent in the flame retardance and the insulating performance after the electrodes are opened/closed, and thus is suitable for the moldings of the circuit breaker. However, in case the thermoplastic resin is applied to the base which is used at the higher temperature and the higher stress than the cover, the handle, etc., especially the base whose temperature exceeds 100xc2x0 C. at the time of current supply and which is subjected to the heavy stress via the crossbar, such thermoplastic resin is not sufficient since the reduction of overtravel in which the creep deformation generated under various conditions between the base and the crossbar takes part mutually is large.
Therefore, as the result of trial and error, the inventors of the present invention found that it is possible to employ the base that has the small reduction of overtravel, in which the creep deformation generated under various conditions takes part mutually, and that contains the thermoplastic resin as a principal component. Thus, the finding will be reported hereinafter.
The present invention has been made to overcome such problems, and it is an object of the present invention to provide a circuit breaker that is capable of decreasing the reduction of overtravel and thinning a thickness of the base and is gentle to the environment.
A circuit breaker according to the present invention comprises fixed contacts each having a fixed contact point; movable contacts each having a movable contact point that is connected/disconnected to/from the fixed contact point; a spring for applying a pushing force to both contact points when both contact points come into contact with each other; a crossbar formed integrally of insulating resin as a principal component to hold the movable contact swingably, and coupled to a lower link of a toggle link mechanism to swing around its swing axis with a motion of the toggle link mechanism; a switching mechanism portion for releasing an accumulated energy of a spring of the toggle link mechanism in response to a handle operation to execute quick-make and quick-break of the movable contact; and a molded case constructed by a base that fixes/supports the switching mechanism portion and a cover covered on the base from a handle side; wherein the base is a moldings that contains thermoplastic resin as a principal component to have a bending modulus of elasticity Eb at an ordinary temperature/ordinary humidity, and the crossbar is a moldings that has a bending modulus of elasticity Ec at an ordinary temperature/ordinary humidity, and following relationships are satisfied.
Eb+Ecxe2x89xa717000 MPaxe2x80x83xe2x80x83(1)
8000 MPaxe2x89xa6Ebxe2x80x83xe2x80x83(2)
9000 MPaxe2x89xa6Ecxe2x80x83xe2x80x83(3)
Therefore, the reduction of overtravel is small, the thickness and the weight of the base can be reduced, and this circuit breaker is gentle to the environment.
Also, the bending moduli of elasticity Eb, Ec satisfy following relationships.
Eb+Ecxe2x89xa7205000 MPaxe2x80x83xe2x80x83(4)
9000 MPaxe2x89xa6Ebxe2x80x83xe2x80x83(5)
9000 MPaxe2x89xa6Ecxe2x80x83xe2x80x83(6)
Therefore, the reduction of overtravel can be further reduced.
Also, the bending moduli of elasticity Eb, Ec satisfy following relationships.
Eb+Ecxe2x89xa725000 MPaxe2x80x83xe2x80x83(7)
9000 MPaxe2x89xa6Ebxe2x89xa622000 MPaxe2x80x83xe2x80x83(8)
9000 MPaxe2x89xa6Ecxe2x89xa617000 MPaxe2x80x83xe2x80x83(9)
Therefore, the reduction of overtravel can be further more reduced, the productivity of molding can be improved, and the outer appearance is excellent.
Also, the thermoplastic resin is at least any one of polybutylene terephthalate, polyethylene terephthalate, polyamide, aliphatic polyketone, polyphenylene sulfide, and their alloy material. Therefore, the circuit breaker is excellent in the chemical resistance and the environment resistance and the recycle can be easily accomplished.
Also, the polyamide is at least any one of nylon 66, nylon MXD6, nylon 46, and nylon 6T. Therefore, the circuit breaker is excellent in the impact resistance and the holding characteristic against the heat generated in the make and break durability test.
Also, the thermoplastic resin is at least any one of polyethylene terephthalate, polyphenylene sulfide, and their alloy material. Therefore, the dimensional change due to moisture absorption is small and the holding characteristic against the heat generated in the make and break durability test is high.
Also, the base contains polybutylene terephthalate of 55 to 70 wt % to which a flame retardant is added, and reinforcement of 30 to 45 wt %. Therefore, the crack is hard to occur when terminals are fastened.
Also, the base contains polyethylene terephthalate of 40 to 70 wt % to which a flame retardant is added, and reinforcement of 30 to 60 wt %. Therefore, the base is excellent in the heat resistance and the creep resistance.
Also, the base contains polyamide of 56 to 60 wt % to which a flame retardant and elastomer are added, and reinforcement of 40 to 44 wt %. Therefore, the base is excellent in the impact resistance and the insulating performance after the shut-off.
Also, the crossbar contains phenol resin as a principal component. Therefore, the crossbar is excellent in the flame retardance and the overtravel characteristic can be improved much more.
Also, the circuit breaker is a multipolar type, and has slits in walls, that orthogonally intersect with a bottom wall of the base, to extend in its wall direction. Therefore, the dimensional change after the molding is small, and the slits can contribute to the reduction of the overtravel.
Also, the slits divide an orthogonal wall to have a uniform thickness. Therefore, it is possible to estimate easily the dimensional change after the molding, and the slits can contribute to the reduction of the overtravel.
Also, the slits are provided alternatively from front and back surface sides of the base. Therefore, the dimensional change after the molding can be further reduced, and the slits can contribute to the reduction of the overtravel.
Also, the orthogonally intersecting walls are interphase walls. Therefore, the walls can contribute to the reduction of the overtravel.
Also, a base thickness between the slits is equal to that of a base bottom wall. Therefore, it is possible to estimate easily the dimensional change after the molding, and the slits can contribute to the reduction of the overtravel.
Also, the orthogonally intersecting walls are a wall provided between a contact point housing portion for housing the movable contact point and the fixed contact point and a switching mechanism housing portion for housing a switching mechanism portion. Therefore, the thermal conductivity from the contact point side to the switching mechanism portion can be lowered, and thus the degradation of the lubricant used in the switching mechanism portion, etc. can be delayed.
Also, the slits are formed to be opened on a back surface side of the base. Therefore, the heat can be radiated effectively.
Also, thicknesses of walls between the slits and an inside of the base are formed thinner than a thickness of the base bottom wall. Therefore, the heat is ready to transfer from the inside of the base to the slits.
Also, the base contains polyamide of 56 to 60 wt % to which a flame retardant and elastomer are added, and reinforcement of 40 to 44 wt %. Therefore, the reduction of overtravel is small, and the thinning and the lightweight of the base can be accomplished, and the base is gentle to the environment. Also, since the thinning of the base can be reduced, the surface insulating distance can be extended. In addition, the base is excellent in the impact resistance and the insulating performance after the shut-off.
Also, the crossbar contains phenol resin of 28 to 32 wt %, reinforcement of 43 to 47 wt %, and inorganic filler of 23 to 27 wt %. Therefore, the reduction of overtravel is reduced much more.
Also, the flame retardant and the elastomer are contained such that halogen compound has a weight percent of 50 to 70 and the elastomer has a weight percent of 20 to 30 to polyamide 100. Therefore, the reduction of overtravel is small, and the flame retardance is high, and the crossbar is excellent in the impact resistance.
Also, the base contains polyethylene terephthalate of 45 to 60 wt % to which a flame retardant is added, and reinforcement of 40 to 55 wt %. Therefore, the reduction of overtravel is small, and the thinning and the lightweight of the base can be accomplished, and the base is gentle to the environment. Also, since the thinning of the base can be reduced, the surface insulating distance can be extended.
Also, the crossbar contains phenol resin of 55 to 65 wt %, reinforcement of 10 to 25 wt %, and inorganic filler of 10 to 25 wt %. Therefore, the molding is easy and the hopper dropping property in the continuous molding is excellent.
Also, the crossbar contains phenol resin of 25 to 35 wt %, reinforcement of 40 to 50 wt %, and inorganic filler of 20 to 30 wt %. Therefore, the reduction of overtravel is reduced much more.
Also, the flame retardant is contained such that halogen compound has a weight percent of 25 to 40 to polyethylene terephthalate 100. Therefore, the reduction of overtravel is small, and the flame retardance is high, and the crossbar is excellent in the impact resistance.
Also, the base contains polyethylene terephthalate of 40 to 70 wt % to which a flame retardant is added, and reinforcement of 30 to 60 wt %, and the crossbar contains phenol resin of 25 to 35 wt %, reinforcement of 40 to 50 wt %, and inorganic filler of 20 to 30 wt %. Therefore, the reduction of overtravel is small, and the thinning and the lightweight of the base can be accomplished, and the base is gentle to the environment. Also, since the thinning of the base can be reduced, the surface insulating distance can be extended. In addition, the base is excellent in the heat resistance.
Also, the base contains polyethylene terephthalate of 40 to 70 wt % to which a flame retardant is added, and reinforcement of 30 to 60 wt %, and the crossbar contains phenol resin of 55 to 65 wt %, reinforcement of 10 to 25 wt %, and inorganic filler of 10 to 25 wt %. Therefore, the reduction of the overtravel is small and the moldability is excellent.
Also, the base contains polyethylene terephthalate of 55 to 70 wt % to which a flame retardant is added, and reinforcement of 30 to 45 wt %. Therefore, the reduction of overtravel is small, and the thinning and the lightweight of the base can be accomplished, and the base is gentle to the environment. Also, since the thinning of the base can be reduced, the surface insulating distance can be extended. In addition, the molding of the fine parts can be implemented. The crack is hard to occur at the time of terminal fastening.
Also, the crossbar contains phenol resin of 25 to 35 wt %, reinforcement of 40 to 50 wt %, and inorganic filler of 20 to 30 wt %. Therefore, the reduction of the overtravel can be reduced much more.
Also, the crossbar contains phenol resin of 55 to 65 wt %, reinforcement of 10 to 25 wt %, and inorganic filler of 10 to 25 wt %. Therefore, the molding is easy and the hopper dropping property in the continuous molding is excellent.
Also, the flame retardant is contained such that halogen compound has a weight percent of 25 to 40 to polyethylene terephthalate 100. Therefore, the reduction of overtravel is small, and the flame retardance is high, and the crossbar is excellent in the impact resistance.
Also, main resin of the base is formed of thermoplastic resin, and slits are provided in walls, that orthogonally intersect with a bottom wall of the base, to extend in its wall direction. Therefore, the dimensional change after the molding is small and the base can contribute to the reduction of the overtravel.
Also, the slits divide an orthogonal wall to have a uniform thickness. Therefore, the dimensional change after the molding can be easily estimated and the slits can contribute to the reduction of the overtravel.
Also, the slits are provided alternatively from front and back surface sides of the base. Therefore, the dimensional change after the molding can be further reduced and the slits can contribute to the reduction of the overtravel.
Also, the orthogonally intersecting walls are interphase walls. Therefore, the walls can contribute much more to the reduction of the overtravel.
Also, a base thickness between the slits is equal to that of abase bottom wall. Therefore, the dimensional change after the molding can be easily estimated and the base can contribute to the reduction of the overtravel.
Also, the orthogonally intersecting walls are a wall provided between a contact point housing portion for housing the movable contact point and the fixed contact point and a switching mechanism housing portion for housing a switching mechanism portion. Therefore, the thermal conductivity from the contact point side to the switching mechanism portion can be lowered, and thus the degradation of the lubricant used in the switching mechanism portion, etc. can be delayed.
Also, the slits are formed to be opened on a back surface side of the base. Therefore, the heat can be radiated effectively.
Also, thicknesses of walls between the slits and an inside of the base are formed thinner than a thickness of the base bottom wall. Therefore, the heat is ready to transfer from the inside of the base to the slits.